Dyeing of tubular knitted fabric has been carried out predominantly with beck dyeing procedures, which are capable of producing quite satisfactory results, but tend to be somewhat capital intensive and inefficient in terms of labor costs, energy costs, effluent disposal problems, etc. Pad batch dyeing, wherein tubular knitted fabric is passed through a low volume of bath of dye solution and subjected to one or more stages of rolling pressure, has been known for some time and has seemingly obvious production advantages. Nevertheless, it has achieved only relatively modest commercial acceptance in the past for tubular fabrics. Recent substantial advances in the art of dye chemistry have begun to make available dyes that are more adequately suited to application by pad dyeing procedures. Nevertheless, for tubular knitted fabrics of 100% cotton, or blends of a high percentage (50% or more) of cotton, pad dyeing has been regarded as relatively unsatisfactory by the industry largely because of potential problems with edge marking.
Edge marking, in pad dyeing of tubular knitted cotton-based fabrics can occur for a number of reasons. Thus, when tubular knitted fabric is processed in tubular form, it typically is handled in flat, two-layered configuration. At the edge extremities, stresses and strains upon the fabric, and specific operating conditions, may differ from other areas of the fabric, resulting in edge lines, which may be either lighter or darker in color. The presence of such edge lines makes the fabric commercially unsuitable, or at least of significantly lower quality than desired by the manufacturer.
In the past, procedures known for pad batch dyeing typically have been either excessively prone to edge marking problems or unduly costly and complex as a result of attempting to avoid such markings. Accordingly, in the past, pad batch dyeing of tubular knitted cotton fabric has not enjoyed significant success.
With the availability of improved dyestuffs, however, greater opportunities exist for the utilization of pad batch dyeing procedures, provided the equipment required is sufficiently simple and reliable, and provided that the equipment can be operated in a production plant environment, by relatively low skilled labor, without excessive problems such as edge marking.
In accordance with the present invention, a significantly improved pad batch dyeing method is provided, in which the principal dyeing action is accomplished by a pair of resiliently covered squeeze rollers, arranged as a horizontally opposed pair, which are disposed partially within a dye solution pan. The arrangement is such that the squeeze rollers are partially submerged in the solution in the pan, but to a level substantially less than one half the diameter of the rollers. A single submerged resilient treating roller is mounted within the solution pan for rolling pressure contact with the front squeeze roller. A guide roller is also mounted within the solution pan, in a position to guide the fabric out of the nip formed by the submerged treating roller and the front squeeze roller and to redirect the fabric upward toward the squeeze nip, formed by the horizontally opposed pair of squeeze rollers. The arrangement provides for the fabric to be acted upon by a single submerged pressure nip, hereinafter sometimes referred to as a dye nip, and for the fabric to be guided by a single submerged guide roller which serves first to convey the fabric away from the dye nip, free of contact with the front squeeze roller, and then to redirect the fabric symmetrically into the squeeze nip in such manner that the fabric does not come into contact with one of the squeeze rollers significantly prior to contact with the other.
In accordance with another aspect of the invention, the fabric advantageously is engaged internally by a ring guide spreader arrangement upstream of and in closely coupled relation to the dye nip. Directly upstream from the ring guide spreader, and in close coupled relation with the spreader, the fabric is engaged by a controllably driven entry feed roller arranged to engage the incoming fabric across its full width and to advance the fabric under positive driving control. This arrangement enables the fabric to be furnished to the ring guide spreader relatively free of lengthwise tension, and enables the fabric to be adjusted by the ring guide spreader to flat, two-layered form and substantially to its normal width. In particular, the fabric is not spread significantly beyond its natural greige width, so that the fabric enters the dye solution with minimum geometrical distortions.
In accordance with a further significant aspect of the invention, the geometrical arrangement of the ring guide spreader and the submerged dye nip is such that the fabric leaving the ring guide spreader proceeds directly into the dye nip, along an entry plane which is approximately at right angles to the plane defined by the axis of the front squeeze roller and the submerged treating roller. Further, the fabric is not diverted by any intervening guide means in its travel from the ring guide spreader to the submerged dye nip, thus avoiding any tendency for the fabric edges to be curled in advance of the dye nip. Likewise, the location of the submerged guide roller advangageously is such as to guide the fabric symmetrically out of the submerged dye nip, and then symmetrically upward into the squeeze nip.
To advantage, the squeeze nip is located above the level of the dye solution, although the lower portions of the squeeze rollers are submerged in the solution. This not only enables the volume of dyestuff in the solution pan to be minimized but provides for an advantageous cascading effect of the dye liquor along the vertically rising fabric, as it emerges from the dye solution and travels upward to the squeeze nip. A further guide roller is advantageously provided at a location spaced well above the squeeze nip, arranged to guide the fabric symmetrically out of that nip.
Among the rather unique features of the invention are that the fabric is acted upon by only a single submerged treating nip and a single submerged guide roller. A number of advantages are derived from this arrangement. First, the required equipment cost is kept at a relative minimum. Second, the basic simplicity of the necessary equipment makes the process particularly suitable for day in, day out production operation by production personnel.
For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment and to the accompanying drawings.